Fuel injection pumps are commonly used in modern engines, such as gasoline engines and diesel engines, to deliver pressurized fuel into engine combustion chambers for combustion. For example, in some diesel engine applications, the pressure provided by the fuel injection pump can be on the order of 104 psi or higher. A typical fuel injection pump may include a cylindrical body having a barrel with a central bore therein and a plunger reciprocating within the bore of the barrel. Due to the need for similar thermal mass for the plunger and the barrel in order to maintain uniform clearance between the plunger and the barrel, the pump barrel is sometimes designed to have thin walls. This may result in a reduced radial stiffness of the barrel. Thus, when the pressure within the bore of the barrel is high, the barrel may undergo radial expansion under the high pressure, and the clearance between the plunger and the barrel may be increased. The increased clearance may cause leakage of fuel and may reduce the volumetric pumping efficiency.
A high pressure fuel injector for a diesel engine is described in U.S. Pat. No. 5,443,209 (the '209 patent) issued to VanAllsburg on Aug. 22, 1995. The fuel injector includes an injector body and a plunger located within a bore of the body, which also defines a pump chamber. When the plunger moves to pressurize the fuel in the pump chamber, the plunger is subject to a high compressive force due to the high pressure fuel. According to the '209 patent, the high compressive force would cause a conventional plunger to expand, and would result in radial expansion of the plunger, causing a reduction in the clearance between the plunger and the inner surface of the injector body. To reduce the radial expansion of the plunger and maintain uniform clearance, the '209 patent discloses a two-piece plunger design. A cylindrical piston is counterbored along its longitudinal axis to a certain depth, and a push rod is located within the counterbored piston. When the plunger is subject to the high compressive force within the pumping chamber, the push rod is allowed to expand radially. Because the radial expansion of the push rod does not affect the outer diameter of the piston, it does not affect the clearance between the plunger and the inner surface of the injector body.
Although the fuel injector of the '209 patent may control the radial expansion of the plunger in order to maintain uniform clearance, it may still be problematic in some applications. For example, the clearance may also be increased due to the expansion of the injector body under high pressure. When the injector body includes thin walls, the high pressure within the pump chamber may cause the thin walls to expand radially. The radial expansion of the thin walls may result in an increase in the clearance between the plunger and the thin walls, which may cause fuel leakage and may reduce the volumetric pumping efficiency of the fuel injector.
The present disclosure is directed toward improvements in the existing technology.